Filter
Top Products
INTRODUCTION TO MCS-85™
SOFTWARE COMPATIBILITY
As
with
any computer system the cost
of
soft-
ware development far outweighs
that
of
hard-
ware. A microcomputer-based system is tradi-
tionally
a very cost-sensitive application and
the
development
of
software is one
of
the key
areas where success or failure
of
the cost ob-
jectives is vital.
8080A
808SA
PROGRAMS
SYSTEM
The 8085A
CPU
is 100% software compatible
with
the Intel® 8080A
CPU.
The compatibility is
at the object or
"machine code" level so that ex-
isting programs written for 8080A execution will
run on the 8085A as is. The value
of
this
becomes even more evident
to
the user who has
mask programmed
ROMs and wishes
to
update
his system without the need for new masks.
PROGRAMMER TRAINING
A cost which is often forgotten is that
of
pro-
grammer training. A new, or modified instruc-
tion set,
would require programmers
to
relearn
another
set
of
mnemonics and greatly
affect
the productivity during development. The 100%
compatibility
of
the 8085A
CPU
assures that no
re-training effort
will be required.
BOBOA
DEVELOPMENT
TOOLS
MCS_85™
8080A
PROGRAM
LIBRARIES
1·8
For the new microcomputer user, the software
compatibility between the
8085A and the 8080A
means that all
of
the software development
tools
that are available for the 8080A and all
software libraries for 8080A will operate
with
the new design and thus save immeasurable
cost in
development and debug.
The
8085A
CPU
does however add two instruc-
tions
to
initialize and maintain hardware
features
of
the 8085A. Two of the unused op-
codes
of
the 8080A instruction set were
designated for the addition so that
100% com-
patibility could
be
maintained.
HARDWARE COMPATIBILITY
The integration
of
auxiliary 8080A functions,
such as
clock generation, system control and
interrupt prioritization,
dramatically reduces
the amount of components necessary for most
systems.
In
addition, the
MCS-85
operates
off
a
single + 5 Volt power supply
to
further simplify
hardware development and debug. A close ex-
amination
of
the
AC/DC specifications
of
the
MCS-85
systems components shows that each
is specified
to
supply a minimum of 400ltA
of
source current and a full TTL load of sink cur-
rent so that a very substantial system can be
constructed
without
the need for extra TTL buf-
fers or drivers. Input and output voltage levels
are also specified so that a minimum
of
350mV
noise margin is provided for reliable, high-
performance operation.
PC
BOARD CONSIDERATIONS
The 8085A
CPU
and the 8080A are not pin-
compatible
due to the reduction in power sup-
plies
and the addition
of
integrated auxiliary
features. However, the pinouts
of
the MCS-85
system components were carefully assigned
to
minimize
PC
board area and thus yield a
smooth, efficient
layout. For new designs
this
incompatibility of pinouts presents no pro-
blems
and for upgrades
of
existing designs the
reduction
of
components and board area will
far offset the incompatibility.